Techniques for inter-storage-processor cache communication using tokens

A method performed at a first storage processing device (SP), the first SP having a first cache, the first SP being communicatively connected to a second SP having a second cache over a cache mirroring bus, the first cache and the second cache being configured to function as mirrors, the first SP and the second SP being configured to operate in an active/active fashion for processing data storage commands directed at a data storage array, wherein the method comprises:

• receiving a write command at the first SP from a host computer directed to a particular address of the data storage array;
• identifying a reference structure in the first cache that is uniquely associated with the particular address, the reference structure pointing to a set of cache pages associated with the particular address, the reference structure having a token count field;
• determining whether the reference structure is synchronized with a corresponding reference structure in the second cache;
• and
• if the reference structure is synchronized with the corresponding reference structure, then:
• performing a cache write operation on a cache page of the set of cache pages pointed to by the reference structure if the reference structure stores a maximum token count value;
• and
• otherwise, sending a token request message from the first SP to the second SP over the cache mirroring bus to request a token from the second SP prior to performing the cache write operation;
• wherein performing the cache write operation on the cache page of the set of cache pages pointed to by the reference structure includes:
• writing data from the write operation into the cache page;
• marking the cache page as containing dirty data;
• sending a replace message from the first SP to the second SP over the cache mirroring bus, the replace message including the cache page on which the cache write operation was performed to be copied to the second cache;
• in response to sending the replace page, receiving a confirmation message from the second SP indicating that the cache write operation has been mirrored into the second cache;
• and
• in response to receiving the confirmation message, sending a confirmation signal to the host computer indicating that the write command has been performed;
• wherein the method further comprises:
• writing data from the cache page marked as dirty to the particular address of the data storage array;
• sending a replace message from the first SP to the second SP over the cache mirroring bus, the replace message including a null cache page pointer and an instruction for the corresponding reference structure to enter a non-synchronized state;
• setting the reference structure in the first cache into a non-synchronized state;
• and
• setting the token count value of the reference structure in the first cache to be equal to one.

A method performed at a first storage processing device (SP), the first SP having a first cache, the first SP being communicatively connected to a second SP having a second cache over a cache mirroring bus, the first cache and the second cache being configured to function as mirrors, the first SP and the second SP being configured to operate in an active/active fashion for processing data storage commands directed at a data storage array, wherein the method comprises:

• receiving a read command at the first SP from a host computer directed to a particular address of the data storage array;
• identifying a reference structure in the first cache that is uniquely associated with the particular address, the reference structure pointing to a set of cache pages associated with the particular address, the reference structure having a token count field;
• determining whether the reference structure is synchronized with a corresponding reference structure in the second cache;
• if the reference structure is synchronized with the corresponding reference structure, then:
• performing a cache read operation on a cache page of the set of cache pages pointed to by the reference structure if the reference structure stores a token count value of at least one and the cache page contains data to be read;
• and
• otherwise, sending a token request message from the first SP to the second SP over the cache mirroring bus to request a token from the second SP prior to performing the cache read operation;
• and
• if the reference structure is not synchronized with the corresponding reference structure, then:
• performing the cache read operation if the reference structure stores a token count value greater than zero and the set of cache pages is not null;
• otherwise, if the reference structure stores a token count value greater than zero and the set of cache pages is null, performing the cache read operation after sending a mirroring request message from the first SP to the second SP over the cache mirroring bus to request the cache page from the second SP;
• and
• otherwise, sending a token request message from the first SP to the second SP over the cache mirroring bus to request a token from the second SP prior to performing the cache read operation.